As the dimensions of semiconductor devices scale down, improving the performance of the semiconductor devices increases in importance and difficulty. One performance issue is the enhancement of the current drive of semiconductor devices. A variety of techniques are known and used in attempts to enhance the current drive of semiconductor devices including gate dielectric thinning, channel length reduction, reduction of the poly depletion, and reduction of the source drain series resistance.
An additional technique for improving the current drive of a semiconductor device includes enhancing the carrier mobility in the channel region of the semiconductor device by straining the silicon in the channel region. A typical and well known method of straining silicon in the channel region of a semiconductor device includes growing multiple layers of silicon and silicon alloys over a silicon substrate of a semiconductor wafer. As illustrated in FIG. 24, this method of straining silicon in the channel region of a semiconductor device includes epitaxially growing a buffer silicon germanium (hereinafter sometimes SiGe) film 104 on a top surface 106 of a silicon substrate 102 of a semiconductor wafer 100. The buffer SiGe film 104 contains a graded germanium (hereinafter sometimes Ge) profile having an increasing amount of Ge atoms toward a surface 110 of the buffer SiGe film 104. A relaxed SiGe film 108 is subsequently epitaxially grown on the surface 110 of the buffer SiGe film 104. The relaxed SiGe film 108 includes SiGe molecules separated from each other at defined distances. A silicon (hereinafter sometimes Si) film 112 is epitaxially grown on a surface 104 of the relaxed SiGe film 108.
Growing the Si film 112 on the surface 114 of the relaxed SiGe film 108 creates a lattice mismatch between the films 108, 112. Due to the lattice mismatch between the Si film 112 and the relaxed SiGe film 108, the Si film 112 becomes strained. In particular, the Si film 112 is under biaxial tensile strain, as shown illustratively in FIG. 25. Further, the Si film 112 is strained in directions substantially parallel to the surface 106 of the Si film 102, as illustrated by direction arrows 114.
Thereafter, the semiconductor wafer 100 may be further processed in a conventional manner to form a semiconductor device 150, for example a MOSFET, as illustratively shown in FIG. 26. In particular, such conventional processing may include doping the source region 118 and the drain region 120 thereby forming a channel region 122 between the regions 118, 120. Such conventional processing may further include the growth or deposition of a gate dialectic 124, for example silicon oxide, a gate terminal or interconnect 126, for example polysilicon interconnects, an insulative material 128, for example silicon oxide, and a plurality of insulative spacers 130, for example silicon nitride spacers.
The aforementioned technique for improving the current drive of a semiconductor device may also improve other performance issues of the semiconductor device. For example, the incorporation of germanium into the semiconductor device may improve the source and drain series resistance. Additionally, other techniques for improving the performance of the semiconductor device may be used in conjunction with the incorporation of germanium thereby improving selective performance issues of the semiconductor device.